Calculating lighting savings.

[Earl Weiss]

The current issue of SSCWN has an interesting Article on lighting savings. The calculations give me a headche but this is where I think I am.

My current rate is .09 a Killowat Hour.

A 320W Scottsdale light is .32KWH so it costs me .0288 an hour to run. (.09x.32).

It seems LSI specs out a Generation 3 retrofit which is 146.5 Watts or .1465KWH or .0131 an hour to run.

Could not find cost of this unit. KR advertises one with seemingly half the LEDs for $500.00.

The LSI Spec sheet shows 11950 Lumens. Could not find the lumens for the 320W Scottsdale.

If I subtract the LED cost of operation .0131 from the Scottsdale .0288 I get a savings of about 1.5 cents an hour. 12hours x 365 days = 4380 hours for a savings of $65.70 a year. (Note this unbit has Occupancy sensing dimming light to 30% power if no one there which would add to savings. Not sure how long it takes to ramp up to full brightness which would be an issue.

If I replace one bulb a year at roughly $35.00 a year that brings the savings to $100.00 a year.

Does this sound right?

Anyone know if the lumen output of the Scottsdale and Gen 3 are comparable?

Anyone have a price for the Gen 3?

If these figures are correct it would take 5 years to recoup the investment.
(My utility and state do not offer any incentives.)

 

[MEP001]

The LSI Spec sheet shows 11950 Lumens. Could not find the lumens for the 320W Scottsdale.

They don't spec the lumens because it varies greatly depending on the bulb (Brand and whether or not it's coated both play a big factor). They're typically around 30,000 lumens.

By your figures, you're cutting your wattage by half, but you're cutting your light by 2/3rds. Your light-per-watt actually decreases, so if you double the lights to compensate you'd actually spend just as much on electricity and still get less light.

I did the same math a couple years ago and figured out that by replacing the 320W ballast and bulb with a 250W I'd save far more money in 15 years than retrofitting to LED. The main factor is the eventual cost of replacing the LEDs again at their end-of-life - at current there's no replaceable LED parts, the whole fixture gets changed out again. If the LEDs lasted 100,000 hours it would be a whole different story, but they last far less than half that.

FWIW, the 250W replacements have maintained their light output MUCH better than the 320W.

 

[bigleo48]

LED is too expensive now for any decent ROI. As discussed before, your biggest bang for your buck is the induction lighting. Do a google search for retrofit kits, and look at lumens, wavelength (color), etc.

The city I live in has retrofitted all the street lights last year and it will pay for itself in just over a year.